I got hold of an old hand-crank phone magneto, and it's actually quite a bit capable! It's fully possible to maintain between 4W and 5W unless it's overloaded, so I decided to hook it up to a rectifier cirquit and step-down regulator to get myself a decent hand-powered 5V DC source.

The rectifier cirquit is dead simple. The generator produces between 50V and 120V AC depending on load (excluding overload), so I first use a 120V to 24V transformer to get a comfortable voltage level (10V-24V). Then I have the diode bridge followed by quite a capacitor made of 5x4700uF caps in parallel. This is needed due to the AC frequency being only about 20Hz (5:1 gear ratio on the crank to coil).

For safety purposes, I added a discharge switch that I can flip to discharge the caps through a 15Ohm resistor rated for 5W. There is also a voltmeter panel I can enable with another switch.

By testing with the 15Ohm discharge resistor connected, it does about 3.75W after the DC conversion for this load (= 7.5V). Brief tests suggest that performance increases with bigger loads, reaching a little above 4W at around 50Ohm load. This is all well above the 0.5A @ 5V specification of the USB 1.0 and 2.0 specs, allthough it won't be able to quickcharge your iPhone.

Finally, the DC-DC converter/regulator is a standard buck-transformer, but I'm still waiting for it to arrive.

If I ever need to power a Raspberry Pi or an Arduino in some odd location far from any power outlet, then I guess that won't be a problem now!

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